Basic present day microcomputers generally include a microprocessor with input-output ports, a read-only memory (ROM) containing permanent microprocessor operating instructions or programs, and a static random access memory (RAM) for temporary storage of data. All components are usually formed on one integrated circuit chip and operate from one common power source.
Most modern random access memories are fabricated with N-channel silicon gate MOS transistors. They are designed for static operation without the need for complex refreshing circuitry, and therefore require a continuous constant voltage source to maintain the states of the memory latches. The data stored in a static RAM will be lost if power is removed or if the applied voltage is even temporarily reduced to the point where the internal memory latches cannot hold their states.
The circuitry of the present invention prevents the loss of memoryy sustaining power if the regular system power supply fails or falters.